sRGB support

[pezcode]

Support for sRGB textures and swapchain would be nice to have. sRGB texture formats will perform the conversion to and from linear RGB in hardware. This is important for loading color images (this excludes normal maps, etc.) which are almost always stored as sRGB, as well as applying the correct gamma transformation for display output. You can do it manually, but that's slow, error prone and enforces bad habits.

Currently, three things are blocking this:

• Swapchain surface format doesn't request _SRGB formats, but _UNORM
• load_texture doesn't support _SRGB formats, even though all 4 formats (RGBA, BC, ASTC, ETC2) have SRGB versions. not sure why they're not supported, maybe there's a good reason I'm not aware of.
• Imgui :< theme colors are defined as sRGB, then interpolated in the shader (which is incorrect), and finally output as mangled sRGB. As a result, storing to an sRGB swapchain image will effectively apply the transform twice. There's an ongoing PR (sRGB support ocornut/imgui#2943) that partly fixes this. This is the real blocking thing here.

Would appreciate some input 😃 Maybe there's a reason you went without sRGB, or you think it's a non-issue.

[TheLavaBlock]

The first two issues should now be fixed.

Request sRGB swapchain if needed:

app.config.surface.formats = { VK_FORMAT_R8G8B8A8_SRGB };

if (!app.setup())
    return error::not_ready;

I don't know what to do about the last one (imgui) at the moment. Let's wait and see what happens there 👀

[TheLavaBlock]

FYI: Added FreeType in 89c95f2 - See Gamma Correct Blending

FreeType assumes blending in linear space rather than gamma space. See FreeType note for FT_Render_Glyph. For correct results you need to be using sRGB and convert to linear space in the pixel shader output. The default Dear ImGui styles will be impacted by this change (alpha values will need tweaking).